Please refer to FIGS. 1A and 1B. FIG. 1A is a schematic illustration of a conventional projection film. FIG. 1B is a schematic structural view of a conventional projection film. In order to prevent the overlapping films from being mutually adhered to each other and not easy to be separated due to vacuum or static electricity and other reasons, both sides of the projection film are provided with a gelatin layer having a thickness of micron (um) level. The surface of the gelatin layer is provided with a plurality of micron-level light-transmission particles (e.g., glass) so that space can be reserved between the overlapping projection films for reducing the effect of vacuum or electrostatic attrition.
Both sides of the projection film are provided with a pattern layer which is relatively non-light-transmissive. A light-transmission portion and non-light-transmission portion are formed on the pattern layer by an exposure pattern process. When a specific portion on a surface of the pattern layer is removed, the light-transmission particles on the surface are also removed without affecting the passage of light. But the light-transmission particles on the other surface still exist.
For example, as shown in FIG. 1B, the conventional projection film 3 includes, in order from the light exit surface to the light entrance surface thereof, a protective layer 3A, a pattern layer 3B, an undercoat layer 3C, a substrate 3D, an antistatic layer 3E and a back coat layer 3F. The surface of the protective layer 3A facing the light exit direction Dout is provided with a plurality of scattered light-transmission particles M. In addition, the surface of the back coat layer 3F facing the light entrance direction Din is also provided with a plurality of light-transmission particles M arranged in a scattered or non-aligned manner.
When the conventional projection film 3 is applied to a projector, since the image is magnified by a high magnification, the pattern is also projected and enlarged to an image with, for example, contract color such being constituted by a black non-light-transmission region and a white light-transmission region according to the relationship between light-transmission portion and the non-light-transmission portion. In addition, the light-transmission particles M may generate impurity on the light-transmission portion as illustrated in FIG. 1A, thereby affecting of the quality of the projection. Therefore, how to remove the projection impurity is an important requirement.